You might wonder what is a network?
If you are looking at this post, you are on a network called internet right now.
Look around, is your computer/desktop/laptop siting around a place like this?
That box with antenna is a wireless router. That blackbox connecting to your cable TV Cable is a cable modem. Most likely, your PC is connecting to your router with an ethernet cable, your router then connects to the cable modem using another ethernet cable, finally the cable modem connects to a cable TV outlet in the wall using a coaxial cable, which is usually known as TV cable. The coaxial cable connects to your internet service provider's network. The internet service provider is the company provides your internet access and most likely TV access as well.
Wait, what if you are reading this post using an ipad, iphone or android? How your mobile devices get internet connection? There are many possibilities, the following two are most common.
One possibility is your mobile device is connecting to that wireless router with wifi. Wifi is a microwave generated by your wireless router and mobile devices, the microwave carries signal so that your device and router are constantly communicating. The content of this post are pass down to your wireless router via TV cable and ethernet cable, then pass to your device via wifi.
Another possibility is your device is connecting to a carrier network like AT & T, verizon, sprint or T mobile. The carrier network also use microwave as the media to pass signal. However, compare to your wireless router's microwave, this type of microwave have shorter wavelength, so it can travel a much longer distance. Long enough to span from your cellphone to the carriers' tower somewhere on the street or on the top of a hill.
Well, something you might not know, your cellphone's battery draws faster when you upload images comparing to when you download images. The reason is, when uploading, your phone generate microwave signal for the tower to receive. Surprise, hah?
Anyway, that's the network we saw with the eyes. Under the hood, tons of things are happening. Next we will explore the network under hood which we can only see with our imagination.